1. Field of the Invention
The present invention relates to a computer system, and in particular, a storage system. More particularly, this invention relates to a computer system that employs an external connection function in a plurality of storage apparatuses. This invention also relates to a management apparatus and a management method for the computer system.
2. Description of Related Art
Storage apparatuses that are computers for providing large-capacity storage resources to host computers are well known. A storage apparatus creates logical storage areas from storage resources and provides them to host computers. The logical storage areas are called logical volumes. A particular kind of logical volume having a virtualized storage capacity is called a virtual volume. Japanese Patent Laid-Open Publication No. 2003-15915 teaches one example of a system using virtual volumes.
The storage control system taught in Japanese Patent Laid-Open Publication No. 2003-15915 has been known for its thin provisioning system. Although having a virtualized storage capacity, each virtual volume has a plurality of address ranges and a host computer designates one of these addresses when issuing a request for write access to a designated virtual volume.
Each time the storage apparatus accepts a write access request, it allocates a physical storage area in a pool volume—one type of logical volume—to the virtual volume and writes write target data in the physical area allocated to the virtual volume.
Thus, the storage apparatus is capable of dynamically expanding the real storage capacity of the virtual volumes and, when some data is no longer necessary, it releases the storage area storing that data from being allocated to the virtual volume and manages the released storage area as an unused physical area.
Accordingly, the thin provisioning system has an advantage of being capable of using the storage resources in the storage apparatus with efficiency when compared to conventional systems that allocate fixed large-capacity storage areas to logical volumes. Incidentally, when it becomes necessary to expand the storage capacity in order to set a new logical volume in the storage apparatus, a new storage device is added to the storage apparatus.
However, the above-described thin provisioning system is intended to enable efficient use of storage resources in individual storage apparatuses, and not intended for enabling, if the storage system includes a plurality of storage apparatuses in addition to host computers, the storage apparatuses to efficiently use each other's storage resources.
Meanwhile, an external mapping/connection system external mapping/connection system for connecting one storage apparatus to another storage apparatus is also known. This system allows a host computer connected to a first storage apparatus to transparently recognize a storage area in a second storage apparatus connected to the first storage apparatus as a logical volume in the first storage apparatus.
However, when it is impossible to connect the second storage apparatus to the first storage apparatus, the first storage apparatus cannot use the storage resources in the second storage apparatus.
In light of the above point, it is an object of this invention to provide a computer system that allows, when the computer system includes a plurality of storage apparatuses employing the external mapping/connection system external mapping/connection system, the storage apparatuses to use each other's storage resources with efficiency.
Another object of this invention is to provide a computer system in which, even if it is impossible to externally connect a second storage apparatus to a first storage apparatus, the first storage apparatus can use a storage resource in the second storage apparatus.